Foams, in this instance foamed fluids, are dispersions of air or other gas as the discontinuous phase in a continuous liquid phase. Usually since the air or gas makes up the larger volume of the foam, the foam bubbles are separated only by a thin liquid film. Unwanted fluid foams are made up of numerous tiny bubbles of a mechanical or chemical origin which are generated within a liquid and accumulate at the liquid surface faster than they decay. The formation of foams can be problematical during the culturing of microorganisms to produce enzymes. If not properly controlled, foam can reduce equipment capacity and increase processing time and expense as well as cause other difficulties, such as loss of biocatalytic activity. For these reasons, antifoaming agents, while being a necessity, are often undesirable or even detrimental when present in downstream processing steps or in the final product.
There are a wide variety of methods available to prepare antifoaming agents. See for instance, "Foam and Emulsion Control Agents and Processes", Colbert, J. C., Noyes Data Corporation, U.S.A., (1981). In the process described by J. B. Plumb, U.S. Pat. No. 3,865,859, Feb. 11, 1975, assigned to Imperial Chemical Industries Limited, England, silicone based polymers are prepared by reacting organochlorosilanes or alkoxysilanes with alkylene or oxyalkylene diols. These polymers, and many other silicone-based polymers, are very useful as surface active agents, particularly for suppression of foam formation in aqueous systems.
The present invention is particularly concerned with the extensive use of antifoams to control foam formation in the industrial production of enzymes. Since enzymes behave as biocatalysts, regulating many of the chemical reactions that naturally occur in living organisms, when isolated, enzymes have many such as in the tanning, detergent, and food industries. Typical industrial production involves incubating an enzyme-producing microorganism in an appropriate culture medium containing salt, a carbon source, a nitrogen source, and an antifoam. After the biomass is separated, the antifoam remains with the enzyme-containing solution, forming a slimy layer as it builds up on ultrafiltration membrane surfaces, greatly slowing the filtration.
It is well known that in general antifoams tend to form a precipitate as they become warmer. Thus, conventional enzyme processing often involves removal of antifoams by employing a heat step prior to ultrafiltration. For instance, the temperature of the entire enzyme solution is raised to 60.degree. C. for several minutes or the enzyme solution is passed over heated coils to give a similar effect. The heating is followed by filtration to remove precipitated antifoam. This process is not only expensive in terms of energy usage, but is not feasible for heat-labile enzymes. In processing situations where heat treatment is not feasible or where heat treatment is not implemented until later stages of processing when the volume to be heated has been greatly reduced, enzyme solutions are kept cool to help the antifoam remain in solution and pass through filtration membranes. However, the great amount of friction occurring in the hollow-fiber membrane systems typically used in this step usually generates enough heat to cause the antifoam to precipitate and eventually clog the filtration membrane.